Question about 1992 Ford F250

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Pedal goes to floor on 92 F250

2nd master cylinder because I thought the first was bad. Bled the brakes 3 times, but still have a pedal that starts out strong then goes slowly to floor. Can't find any leaks either. Please help. Reg.

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  • schrizo Oct 31, 2008

    To all who are helping with this brake problem thank you. I am confused about the power booster and how it could cause this issue. Since it is the only place I have not looked, I now think it is related. Even if the booster has an issue how is it that it could push the master plunger via the brake pedal to the floor.? I assume I am pushing the air rather than the master plunger. Thanks again guys.

  • schrizo Feb 07, 2009

    Grabber GT. That was one solution I have not heard. Thanks. Not sure when I can get at it as it is winter here and cold. I had this truck into a brake shop and they went through 4 master with the same results. It was embarrassing returning all those masters. They never could fix it and gave up. So, I have bled that anti lock cylinder but have not replaced it, so it may be my best best. Thanks dude.

  • schrizo Feb 07, 2009

    Grabber GT-finally a most resonable answer. IT has been a most troubling problem as my freind works in a parts place and I have returned "sheepishly" 3 masters to him. Without any leaks it has been the only solution anyone could come up with. Do you think a jusk yard RABS would be worth a try?? It is an old truck and does not get used much as it is a diesel and sucks expensive fuel. Thanks again and if this works I will let you know. It may be a while. Reg.

  • schrizo Feb 08, 2009

    absolutely, I found that out when getting the master. I suppose Ford would have detected the problem right away as you did working for them. So many variables when working with the anti lock brakes. I pull a heavy trailer from time to time and I was worried as a problem with the brakes could be very bad. Take care.

  • schrizo Mar 07, 2009

    hello

  • schrizo Mar 07, 2009

    Hey Grabber. The weather finally broke here and I went to work on the brakes. I read on another thread about a guy you said to remove the nut on the RABS valve and remove the spring, put the nut back on and try the brakes. I was able to get pressure then. So, it seems you were right but I have another question. Do you see any harm in running the truck without that spring?? I think the only problem would be the anit locks won't work. But thanks man. I appreciate it a lot. Reg.

  • schrizo Mar 09, 2009

    Thanks Doug. 2 thumbs up.

  • xjxtc May 03, 2009

    I'm working on a 1992 Ford F-250 Custom 4x4 5.8L - I've installed a new master cylinder, front brake pads, bled the lines until there's no air in the lines and I'm getting clear fluid, and the brake pedal still goes to the floor when it's running and you hold your foot on the pedal. There are no signs of any leaks, and I'm running out of ideas, any help??

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I would strongly recommend checking your trucks R.A.B.S. (Rear Antilock Brake System) valve . It is located on the left frame rail just under where your left foot would rest . They can leak internally and exhibit the problems you are describing (loss of pedal , with no fluid loss) .
It is highly unlikely that a power booster would cause this , as a failed booster will show itself in these ways . 1) a hissing sound when you apply the brakes (indicates a vacumm leak) 2) rough engine idle/stalling when brakes applied (also indicates a vacumm leak) or 3) No power assist (brake pedal hard to push) .
If you do discover your hydraulic problem is in your RABS valve , don't forget to bleed it ,(there is a bleeder valve on it) and the rear brakes again after you replace it .
Hope this helps
Doug

Posted on Feb 06, 2009

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  • GrabberGT Feb 07, 2009

    You're very welcome .

    I also forgot to tell you that they (RABS valves) can leak internally and not turn on the "Rear-Antilock" light on your dash.

    Back in my younger days (when your truck was new) , I worked at a Ford dealer and found defective RABS valves frequently, and that was usually after the owner (or another mechanic) replaced the master cylinder a few times and bleed the brakes in an attempt to solve the problem you are describing .

    Doug

  • GrabberGT Feb 07, 2009

    A wrecking yard unit is worth a shot, but remember , you have no way of knowing 100% if that unit is good . Also be sure to get one off of a truck who's Gross Vehicle Weight Rating is similar to yours, as Ford does change the size of them for different weights (and this is most common on F-250). There are really only 2 units , so don't let what I just said scare you . There is the unit for trucks with a GVW over 8600 and a unit for trucks under 8600.

    Doug

  • GrabberGT Mar 09, 2009

    As far as removing the spring in the RABS valve, you're correct that the Antilocks won't function now , however, if you now have a good pedal and no other external leaks , the brakes should now function.

    As to my recommending that as a fix. I can't recommend that, (although on a temporary basis you'd be ok until you get the RABS valve replaced) . The fact is that it may work fine that way for the life of the truck , but should an accident ever occur, and some attorny discovered that you've tampered with the truck's braking system , you may be liable for damages .

    Glad to have helped

    Doug

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Well with a soft braking pedal it means its a lost of pressure problem somewhere in the braking system. If you changed the master cylinder (with a brand new one not used) and blead the brakes check the disc pads and shoes then there is a leak somewhere in the system. Start from the braking fluid work your way in the master cylinder then through the lines you will find it. One way to check if the master cylinder is loosing compression is to

1.) Take the cap of the brake fluid container
2.) start the car leave it in park or neutral
3.) have some push the braking pedal right down as they are doing this look for air bubbles in fluid container, in some cases you will need to pump the braking pedal to see any bubbles.

Another method is used by pumping the brake pedal to see if it hardens up. Usually i find this problem to be caused by rubber seals in the master cylinder. usually one or more of them is damaged. You can repair the master cylinder by using a kit for it sold at automotive stores.

If the cylinder is brand new you have a small air leak some where in the lines causing the lost of compression. It might just be small enough to leak air with small amounts of fluid that may not be noticed. (it dont have to be by the wheels it could be anywhere along the lines) you may want to consider doing a compression test at a service station to see if this is so.

Posted on Oct 31, 2008

  • Rishi Roshan Ali Oct 31, 2008

    I assumed the booster is built together with the master cylinder in case yours is seperate then check that as well

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If there is no fluid loss, most likely there is still air in the system. Did you bench bleed the master cyl before installation? How are you bleeding the system?? Manual or power bleed? Also pull a vacuum test on the booster

Posted on Oct 31, 2008

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This sounds like the vacuum in the brake booster has a leak. The big part that mounts to the firewall and has the master cylinder mounts onto it.. (i think)
The booster uses vacuum to assist with the breaking. It is mostlikely the culprit.

Best wishes..

Posted on Oct 31, 2008

  • Double D
    Double D Nov 01, 2008

    The brake Booster is just a catalyst, a middleman, that helps you push into the master cylinder, and in effect, compres the hydraulic fluid (brake fluid) to push the brake calipers against the drum or disc. it pushes harder against the master cylinder so you don't have to.

    If the booster were to absolutely fail you will still have the ability to brake.. just not as easily.

    The manufacturer would never design the brake system to just simply stop working, instead they designed it to allow you to safely stop.. even though it would be harder to do and require more physical effort and would travel all the way to the floor..

    btw.. how is my reply "inappropriate" ?

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